Penetration Thresholds Research Articles

Growth of aligned ZnO nanorods on woven Kevlar® fiber and its performance in woven Kevlar® fiber/polyester composites

ZnO nanorods were grown by a seeding treatment on surface-functionalized woven Kevlar® fiber (WKF), and the decorated WKF was used to prepare composites with polyester resin (PES) via vacuum-assisted resin transfer molding. Fourier transform infrared spectroscopy (FT-IR) confirmed the surface functionalization of the WKF. The characteristic peaks of ZnO observed by FT-IR and X-ray diffraction (XRD) indicated the growth of ZnO nanorods on the surface of the WKF. FT-IR analyses of the composites were consistent with an interaction between the WKF, and ZnO and PES. The intensity of the XRD peak for crystalline ZnO increased with increasing growth of the nanorods. The morphology of the nanorods was studied by scanning electron microscopy. The growth of the nanorods increased with increasing treatment time. Thermogravimetric analysis also supported the growth of nanorods. The presence of ZnO nanorods significantly improved the impact resistance of the WKF/PES composites; the penetration thresholds were also determined. The WKF/ZnO/PES composites had substantially higher tensile strengths and moduli than the ZnO-free composites.

Clean Generation Technologies in Chinese Power Sector: Penetration Thresholds and Supporting Policies

As one of the top energy consumption country, China is under huge pressure of energy security, GHG emission control and environmental protection. Accounting for half of China energy-related emission, Chinese power sector especially need a quick development of clean generation technologies. However, the current developing speed is not enough and the crucial development thresholds of clean generation technologies are poorly understood. For these reasons, this study uses MESEIC (Multi-regional model for Energy Supply system and their Environmental ImpaCts) model to offer a suggested roadmap for Chinese power sector. Through different scenarios, this study sheds light on the penetration thresholds of various clean generation technologies and put forward policy suggestions in different time-scale for breaking out the thresholds. Setting solar power case as an example, the short-term threshold is its generating cost. The suggested solution is enacting promotional policies, such as feed-in tariffs (0.45 RMB/kWh), renewable portfolio standards, renewable energy certificate trading, tax based incentives etc. The long-term threshold is geography limitation, which can be solved by improving the power grid transmission capacity and developing distributed solar energy.

Thickness-dependent energy dissipation characteristics of laminated composites subjected to low velocity impact

This study investigates the low velocity impact properties such as damage thresholds, critical energy thresholds and damage process of laminated composites. Damage thresholds of Hertzian failure and main failure corresponding to woven and unidirectional Glass Fiber Reinforced Polymer laminates in varying thicknesses from 2mm to 8mm are determined through impact tests with nominal impact energies of 4, 6, and 8J/layer. Hertzian failure and main failure thresholds of a composite laminate with a particular thickness remain substantially constant with the nominal and incipient impact energies. Energy profile and normalized energy profile diagrams are used to find out the penetration and perforation thresholds as well as explaining the correlation between the threshold energies and damage process of the laminates. Dissipated energy by a laminate is determined using a second order polynomial regression based on the relationship between energy dissipation and impact energy of data points before penetration. Penetration and perforation energies increase non-linearly with the thickness and thickness dependence is expressed using a power regression. Test results related to damage thresholds, threshold energies and effective damage area reveal that unidirectional laminates possess lower impact damage resistance and hence are more sensitive to impact damage.

Core-thickness effect on the impact response of sandwich composites with poly(vinyl chloride) and poly(ethylene terephthalate) foam cores

The objective of this study was to investigate the effects of core material and its thickness on impact behavior of sandwich composite plates subjected to low-velocity impact, experimentally. Poly(vinyl chloride) (PVC) and poly(ethylene terephthalate) (PET) foams were selected as the core material, having approximate density of 65 kg/m3 and 60 kg/m3, respectively, and thicknesses of 5, 10, and 15 mm. The stacking sequence of the sandwich composites is [Formula: see text] Impact tests were carried out by using Ceast 9350 Fractovis Plus impact testing machine under room temperature. Various impact energies were selected ranging from 10 J to 70 J to analyze the impact energy level. The dimensions of the specimens are 100 mm × 100 mm. After the impact tests, contact-force deflection curves and also maximum contact force, maximum contact time, and maximum deflection versus impact energy curves were obtained for mentioned impact energies for sandwich composites with PVC and PET foams and [Formula: see text]-laminated composites. As a result, it is seen that the core material and its thickness have notable effects on the impact behavior of sandwich composite plates. Sandwich composites also have higher absorbed energy, penetration, and perforation thresholds.

Impact characterization of thermoformable fibre metal laminates of 2024-T3 aluminium and AZ31B-H24 magnesium based on self-reinforced polypropylene

In this work, the impact behaviour of an AZ31B-H24 magnesium-based fibre metal laminate (FML) and a 2024-T3 aluminium-based FML with self-reinforced polypropylene (SRPP) is analysed. The study focused on determining the impact properties of the FMLs and explaining the differences between their impact responses. Additionally, in the comparative study, a single SRPP was included as reference base material. Low-velocity impact tests were performed by using a drop-weight machine. The failure energy for cracking of metal sheets, onset of fibre breakage in the composite constituent and total perforation of the laminate were identified by correlating force–time curves measured from impacts with images of impacted specimens obtained by a macroscope. Moreover, the ‘energy profile method’ was used to identify the penetration and perforation thresholds enabling the definition of the no-penetration and the penetration phases. The results revealed that the Al-FML presented more specific resistance and energy dissipation capacity under impact than the Mg-FML.

Impact response of composite plates manufactured with stitch-bonded non-crimp glass fiber fabrics

Abstract This experimental study deals with the impact response of composite plates manufactured with stitch-bonded non-crimp glass fiber fabrics. Three kinds of fabrics – biaxial, triaxial, and quadraxial – are used as reinforcing material. Polyester resin is used as a matrix material in the composition of composite plates. An instrumented drop weight impact testing machine, Instron-Dynatup 9250 HV, is used for impact testing. Impact tests are performed under various impact energies, ranging from damage initiation to final perforation. An energy profiling method, showing the relation between impact energy and absorbed energy, was used together with load-deflection curves to determine the penetration and perforation thresholds of those composites. The failure processes of damaged specimens for different impact energies were evaluated by comparing load-deflection curves and images of damaged samples taken from the impacted and non-impacted sides. All types of composites have obvious penetration and perforation thresholds. The perforation threshold of triaxial/polyester composite is approximately 27% and 22% higher than that of the quadraxial and biaxial/polyester composites, respectively.

The effect of temperatures on hybrid composite laminates under impact loading

The present experimental investigation deals with the impact responses of hybrid composites (carbon–glass fiber/epoxy) under various temperatures. A number of samples were subjected to increasing impact energy at the temperature range of −20 to 60°C until complete perforation of samples. With this use of increasing impact energies, it was possible to examine the impact response and failure mechanisms of hybrid composites until perforation of sample. An Energy Profiling Diagram (EPD) was used to obtain the penetration and perforation thresholds of hybrid composites. Besides, the temperature effects on impact characteristics such as load, contact time and permanent deflection were also presented in figures. Test results showed that temperature variations affect the impact characteristics of hybrid composites and they get their maximum values at −20°C or 60°C.

An experimental investigation on the impact behavior of hybrid composite plates

Abstract In this experimental study, the impact behavior of hybrid composite plates has been investigated. The increasing impact energy was performed on two types of hybrid composite plates (glass–carbon/epoxy) until complete perforation of specimens. An energy profiling method, showing the relationship between impact energy and absorbed energy, was used together with load–deflection curves to determine the penetration and perforation thresholds of hybrid composites. The failure processes of damaged specimens for different impact energies were evaluated by comparing load–deflection curves and images of damaged samples taken from impacted sides and non-impacted sides. Cross-sections of damaged specimens were also inspected visually and discussed to assess the extent of damage, such as fiber fracture in layers, expansion of delaminations between adjacent layers. The perforation threshold of hybrid composite impacted from surface with carbon fibers was found approximately 30% higher than that of surface with glass fibers.

Effect of the Size of Aggregates on Pore Characteristics of Minerals Measured by Mercury Intrusion and Water-Vapor Desorption Techniques

AbstractThe size, shape, and continuity of pores in mineral solids greatly influence the behavior of percolating liquids and solids in porous media, which has significant practical environmental implications. In order to expand understanding of these properties in soil minerals, the present study was undertaken to analyze the pore characteristics of bentonite, illite, and kaolinite in the forms of powder and aggregates of different dimensions, combining water-vapor desorption and mercury-intrusion techniques. Different granulometric fractions of milled quartz glass were also studied. With increasing aggregate size of the minerals, larger pore volumes (up to 25%), smaller surface areas (down to 15%), larger average radii (up to 15%), and smaller fractal dimensions (down to 6%) were measured using water-vapor adsorption-desorption data. The differences were smallest for bentonite, possibly due to the smallest particle size of this mineral and/or to its very large water-vapor adsorption capacity. The degree of water-vapor adsorption on quartz was too small to rely on the data obtained.The pore volumes and average radii, measured by mercury-intrusion porosimetry, were up to few times larger for the mineral powders than for their aggregate counterparts. Similar values were noted for aggregates >1 mm in diameter, for which the input of interaggregate spaces into total porosity of the sample bed was negligible. Two pathways of mercury intrusion were detected in porosimetric curves: filling of interaggregate spaces, and penetration into aggregates. Similar penetration thresholds into aggregates of different sizes were calculated. With increasing size of quartz grains, the pore volume of the quartz bed decreased whereas the average pore radius increased. Mercury intrusion detected pore-fractal behavior of bentonite and kaolinite, but for aggregated minerals the calculated values of fractal dimensions were >3, values which increased with increasing aggregate size. Very similar pore parameters were measured for aggregates prepared from a natural deposit of kaolinite and for artificially prepared aggregates from powder of the same mineral, indicating that artificial aggregation can simulate natural processes.Both water desorption and mercury intrusion detected fractal behavior in the limited range of pores. A test to find fractal build up of the aggregates in extended scales based on a dependence of surface area of unit volume of aggregate bed on aggregate size showed no fractal-aggregate build-up.

An Experimental Investigation on the Impact Behaviour of Glass/Epoxy and Hybrid Composite Plates

In this study, the impact behaviours of glass/epoxy and hybrid (glass-carbon/epoxy) composite plates have been investigated experimentally. The increasing impact energy was performed on composite plates until complete perforation of samples. An energy profiling diagram, showing the relationship between impact energy and absorbed energy, was used together with load-deflection curves to determine the penetration and perforation thresholds of composite plates. The failure processes of damaged specimens for different impact energies were evaluated by comparing load-deflection curves and images of damaged samples taken from impacted sides and non-impacted sides. Cross-sections of damaged specimens for both plates were also inspected visually and discussed to assess the extent of damage, such as fibre fracture in layers, expansion of delaminations between adjacent layers. The perforation threshold of hybrid composite impacted from surface with carbon fibres was found approximately 30% and 15% higher than those of surface with glass fibres of hybrid plates and glass/epoxy plates, respectively.

A new damage index to monitor the range of the penetration process in thick laminates

A damage variable (damage degree DD) representing the ratio between the absorbed energy and the impact energy was introduced in 1998 by Belingardi and Vadori to assess damage accumulation caused by low velocity impacts. More recently, repeated impact tests carried out on thick laminates pointed out the significance and extent of the penetration process in thick laminates, which the DD is unable to monitor as, by definition, it reaches the value of one at penetration to remain unchanged over the entire penetration process. In the present paper, a new damage variable (damage index DI) is proposed to overcome shortcomings of the DD with respect to thick laminates. By introducing the displacement of the impactor into the definition of the DI, the depth of the penetration process is taken into account. Normalization by the displacement of the quasi-static perforation test allows for a non-dimensional damage variable which is shown to reach the value of one at perforation. Validity of the approach is proven against impact data obtained for different fibre-matrix architectures and laminate thickness. Results show that the DI can effectively differentiate between penetration and perforation thresholds, increasing monotonically within the range of the penetration process. In particular, the DI is shown to increase linearly with the impact energy up to penetration and to rise quite abruptly within the range of the penetration process. Results for repeated impact tests prove that at first the DI increases quite linearly impact after impact, owing to a steady accumulation of damage. A few impacts before penetration a sudden rise in the DI value points out a change in the rate of damage accumulation.

Effect of Neoclassical Toroidal Viscosity on Error-Field Penetration Thresholds in Tokamak Plasmas

A model for field-error penetration is developed that includes nonresonant as well as the usual resonant field-error effects. The nonresonant components cause a neoclassical toroidal viscous torque that keeps the plasma rotating at a rate comparable to the ion diamagnetic frequency. The new theory is used to examine resonant error-field penetration threshold scaling in Ohmic tokamak plasmas. Compared to previous theoretical results, we find the plasma is less susceptible to error-field penetration and locking, by a factor that depends on the nonresonant error-field amplitude.

Impact response of woven composites with small weaving angles

This paper presents experimental investigations on impact response of woven composites with various weaving angles between interlacing yarns. A method for preparing novel woven composites with small weaving angles is presented. The effects of the weaving angle on the impact characteristics such as peak force, contact duration, maximum deflection and absorbed energy are also examined. An energy profiling method seems to be useful for identifying the penetration and perforation thresholds of the woven composites. The damage process of individual woven composites can be reconstructed from comparing the corresponding load–deflection curves, energy profile and images of damaged specimens. The study concludes that the energy absorption capability and perforation threshold of woven composites can be significantly improved by using a small weaving angle between interlacing yarns. For example, the perforation threshold of [0/20] 4 woven composite, which has a weaving angle of 20° between interlacing yarns, is about 40% higher than that of [0/90] 4 woven composite, which has a weaving angle of 90° between interlacing yarns. The higher energy absorption capability of [0/20] 4 over [0/90] 4 is attributed to a lower stiffness caused by a more polarized fiber orientation and a smaller fiber crimp, resulting in a larger maximum deflection, a more extended damage zone and a larger amount of fiber pullout.

Low Velocity Impact Response of Small-Angle Laminated Composites

Reducing delamination is essential in increasing the impact resistance of laminated composites. In this study, two methods were used to improve energy-absorption capabilities of laminated glass/epoxy composites; one was based on small fiber angle changes between adjacent laminae, and the other was based on through-thickness stitching reinforcement. Penetration thresholds were determined for small-angle laminated composites [0/θ] 6 for which θ = 0, 5, 10, and 15 deg. The small-angle laminated composites, especially [0/15] 6 , were found to have higher penetration thresholds than the conventional large-angle laminated composites, such as [0/90] 6 , due to damage progression (most notably, fiber bridging). Stitched small-angle laminated composites were also found to have higher impact resistance than unstitched specimens with the same stacking sequence. The use of small-angle composites was extended to multi-axis laminated composites, such as biaxis, triaxis, and sexiaxis laminated composites. Penetration thresholds of the multi-axis laminates were found to be very comparable with the uniaxis laminated composites, that is, [0/θ] 6 .

Simulation of Soft Projectiles Impacting Composite Targets using an Arbitrary Lagrangian-Eulerian Formulation

Methods for modeling the impact of triaxial braided composites with a gelatin projectile have been developed using the commercial explicit finite element code LSDYNA. An arbitrary Lagrangian-Eulerian formulation was used to resolve problems with numerical instability that were encountered in previous simulations based on a pure Lagrangian formulation. The LSDYNA MAT 58 material model and shell elements were used for the composite. Composite material properties were obtained from available experimental data and micromechanics calculations. The impact dynamics and penetration thresholds observed in the experiments were adequately simulated. The simulated contact forces between the projectile and composite material were useful for understanding the onset of penetration. The effect of boundary conditions on the penetration threshold was simulated using spring elements located at the boundaries. Simulations confirmed experimental observations that the penetration threshold is higher when slipping occurs during the impact. The impact simulations also show that the reaction forces at the boundaries of the half-ring are much smaller than for the flat plates, and so the boundary slipping will occur more likely during the flat plate impact case.

Technology choice and timing with positive network effects

When two competing and incompatible products coexist in a market, potential users face a choice between the two products and the alternative of deferring the decision. This paper examines the choice between the two substitutes, where each one is subject to a positive network effect. That is, a user of one of the products experiences an increase in the value for each additional person using the same product. We examine this buy or wait problem, either for an individual or a manager making the investment on behalf of a firm, by formulating and analyzing a decision-theoretic model. To model the stochastic evolution of market share, we build on the generalized Polya urn of Arthur et al. [Arthur, W.B., Ermoliev, Y.M., Kaniovski, Y.M., 1987. Path-dependent processes and the emergence of macro-structure. European Journal Of Operational Research 30 (3), 294–303], allowing for composition of the market to affect not just the relative market shares but also the absolute growth rate of the market. We show that the optimal strategy is defined by a pair of market penetration thresholds that depend on the market composition. Looking at the effect of the network effects on the optimal strategy, we find that more pronounced network effects can either raise or lower the penetration thresholds.

Market penetration metrics: tools for additionality assessment?

Abstract Project-based emission reduction or ‘offset’ programs are being implemented widely, from the CDM (Clean Development Mechanism) to corporate voluntary efforts and municipal and state-level activities. Additionality assessment remains a central and persistent challenge in all programs. Concerns have been raised with methods currently used, such as investment analysis, barrier analysis, and performance thresholds. They have been variously critiqued for high costs, resistance to standardization, weak environmental integrity, and susceptibility to gaming. Technology penetration rates provide another means to infer additionality, and could be a potentially useful complement to other methods. The notion is that emerging technologies with low but increasing penetration rates typically require some type of support, as might be provided through offsets markets, to compete effectively in the marketplace. For penetration rate analysis to provide a useful tool for additionality assessment, several fundamental questions need to be addressed. What do penetration rates represent and how can they be measured? How can additionality evaluation utilize penetration rates? For which sectors and project types are the use of penetration rates most promising? This article shows that penetration tests have a mixture of pluses and minuses, with greater relevance in certain market niches and regions. Reasonable ranges for penetration thresholds are discussed, along with partial crediting approaches to reduce ‘knife-edge’ effects.

Characterization of Impact Properties and Damage Process of Glass/Epoxy Composite Laminates

This paper investigates the responses of glass/epoxy composite laminates subjected to impact loading. It presents a new technique to characterize the impact properties and to correlate them with the damage process of the composite laminates. The technique, called the energy profiling technique, is based on instrumented impact tests and the least-squares method. The technique gives specific definitions of the penetration and perforation thresholds of the composite laminates. It also defines the range of the penetration process and quantifies the energy absorption efficiency of the composite laminates. The primary damage modes in the damage process of the composite laminates can also be correlated with the impact properties by using the energy profiling technique. The advantages of using this technique to analyze the experimental data obtained from impact tests are demonstrated by investigating the glass/epoxy composite laminates with various impactor sizes, laminate thicknesses, fiber orientations, and a sandwich construction. Results from the energy profiling technique show that the penetration and perforation thresholds increase nearly linearly with the size of the impactor while they increase nonlinearly with the thickness. A sandwich composite made of two glass/epoxy laminates and a foam material is found to have higher energy absorption efficiency than a bonded laminate. Among the five [05/ θ5/05] composite laminates investigated, where θ = 0, 15, 30, 45, and 90, [05/155/05] has the highest resistance to delamination and has the highest penetration and perforation thresholds. All these results clearly indicate the advantages of using the energy profiling technique for the analysis of composite laminates subjected to impact loading.

Impact resistance of common spectacle and safety lenses to airgun and rimfire projectiles

Purpose To evaluate the penetration resistance of common spectacle and safety lenses to high-velocity projectiles and to examine the current recommendations regarding the use of such lenses. Methods The penetration threshold of glass, high-index, and polycarbonate spectacle and safety lenses was determined by firing BBs, pellets, and 0.22-caliber projectiles. The mass, diameter, velocity, and energy of each projectile were measured, and the center thickness, mass, and refractive power of each lens were recorded. The penetration threshold for each lens type was calculated, and a comparison of impact resistance was made. Results The maximum velocity of the BB was measured at 221 m/s; pellets at 210 m/s; CB.22 rimfire projectiles at 204 m/s; and 0.22 rimfire projectiles at 290 m/s. The BB penetration thresholds were as follows: glass lenses = 84.0 m/s (2.4 J) and high-index lenses = 107.7 m/s (4.09 J). Polycarbonate spectacle and safety lenses were not penetrated by BBs regardless of their velocity; however, these lenses were penetrated by CB.22 rimfire projectiles (89.2 J). Review of the penetrated lenses showed that center thickness and refractive power was comparable between the various groups of projectiles. Conclusions Polycarbonate offers a vastly superior degree of penetration resistance compared with other commonly used lens materials. The current recommendations regarding the use of polycarbonate in prescription and protective lenses, as endorsed by the American Academy of Ophthalmology and the American Academy of Pediatrics, must be reevaluated.

Plasma parameter scaling of the error-field penetration threshold in tokamaks

A previously published analytical formula for the error-field penetration threshold in rotating tokamak plasmas is successfully benchmarked against nonlinear magnetohydrodynamical simulations in slab geometry. Moreover, the fundamental assumption underlying the derivation of this formula, namely, that the response of a flowing plasma to a low amplitude, quasistatic, resonant magnetic perturbation is governed by linear, constant-ψ layer physics, is verified over a wide range of plasma parameters, which includes the parameter range relevant to Ohmic and neutral beam injection start-up discharges in modern-day tokamaks. It is concluded that the formula in question can be used to estimate error-field penetration thresholds in such plasmas.